subversion: improve build time (use deparallelize only when necessary)

Closes #20602.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
subversion 1.8.0

Closes #20600.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
libsass: silent update back to previous sha1
zsh: generate helpfiles for run-help

Closes #20589.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>